Multilayer optical disk, and method and device for recording optical information thereon

ABSTRACT

A disc capable of reproducing an address signal and a data signal correctly even by using a multilayer optical disc that includes a plurality of recording reproduction surfaces bonded together in a state in which front positions in sectors of the respective recording reproduction surfaces do not match completely, a method and a device are provided. In one embodiment, a relationship between a bonding precision L and a length G of a gap area is determined to be L≦G. In another embodiment, by recording information in a range of a length corresponding to the bonding precision L not only in the data area but also in the gap area, a data recording starting position and a data recording ending position for each sector of the respective recording reproduction surfaces are matched. In yet another embodiment, guard areas are provided in a tip portion and a back end portion of the data area.

This application is a 371 of PCT/JP00/02159, filed Apr. 3, 2000.

TECHNICAL FIELD

The present invention relates to a multilayer optical disc having aplurality of recording reproduction surfaces, a method and a device forrecording optical information in this multilayer optical disc.

BACKGROUND ART

A conventionally known multilayer optical disc capable of recording onand reproducing from a plurality of recording reproduction surfaces isdescribed, for example, in JP 10(1998)-505188A.

In the following, the structure of a conventional multilayer opticaldisc will be explained by referring to the drawings. FIG. 7 is across-sectional view showing a conventional optical disc 10 taken in thedirection perpendicular to the track direction. In addition, forsimplifying the explanation, an optical disc of a double layer structurewill be used.

As shown in FIG. 7, a guiding groove 7 for tracking (alternatively, anaddress signal recorded in advance and formed as a pit) is formed on onesurface side of a first substrate 1, and further on this surface, arecording reproduction film for partially reflecting and partiallytransmitting an optical beam 8 entering the first substrate 1, focusedby an objective lens 9, is formed to create a first recordingreproduction surface 3. Furthermore, a guiding groove 6 for tracking(alternatively, an address signal recorded in advance and formed as apit) also is formed on the surface of a second substrate 2, and arecording reproduction film for reflecting the optical beam 8 passingthrough the first recording reproduction surface 3 is formed to create asecond recording reproduction surface 4. Furthermore, a separating layer5 is interposed to separate the first recording reproduction surface 3and the second recording reproduction surface 4 and to bond themtogether.

However, the multilayer structure as mentioned above (double layerstructure in the conventional example) suffers from the followingproblem when the bonded state in the cross-sectional view takenperpendicular to the aforementioned cross-sectional view, that is in thetrack direction, is as that shown in FIG. 8.

In addition, for explanatory purposes, FIG. 8 expresses the actualsector structure (shown in FIG. 9(b)) of a multilayer optical disc,which is shown as a plan view in FIG. 9(a), in the form of a schematicsector structure for each recording reproduction surface.

FIG. 9(b) is, as shown in FIG. 9(a), an enlarged view of the vicinity ofan address area 92 in a certain track among a group of tracks 91 formedas concentric circles or spirally in the multilayer optical disc, andshows a part of a groove portion 93 in the (n−1)th sector, an addresspit portion 941 corresponding to an address area of the nth sector to bedescribed later, and a part of a groove portion 942 in the following nthsector 94. This groove portion, expressed in the form of a schematicsector structure, is divided into a gap area and a data area to bedescribed later.

Moreover, the constituent elements shown in FIG. 7, i.e. the firstsubstrate 1, the second substrate 2 and the separating layer 5 areomitted in FIG. 8 for explanatory purposes.

In FIG. 8, 31 is a first recording reproduction surface, and 41 is asecond recording reproduction surface. 311, 312 and 313 respectively arean address area, a data area and a gap area for dividing the addressarea 311 and the data area 312 in the first recording reproductionsurface 31. Moreover, 411, 412 and 413 respectively are an address area,a data area and a gap area for dividing the address area 411 and thedata area 412 in the second recording reproduction surface 32.

The gap areas 313, 413 are provided to perform a signal processing, whena recording and a reproduction for a multilayer optical disc areperformed by a drive, by clearly separating a reproduced address signaland a reproduced data signal of a data area, and by avoiding the gapareas 313, 413, the recording operation is performed respectively forthe first recording reproduction surface 31 and the second recordingreproduction surface 41.

However, as shown in FIG. 8, when the heads of the address areas 311 and411, that is, the front positions of sectors are bonded together by ashift L1, and when this amount of shift L1 is larger than a length G1 ofthe gap areas 313 and 413, an area Δ1, which is an area at the rear endportion in the address area 311 of the first recording reproductionsurface 31, overlaps with an area Δ2, which is an area at the front endportion in the data area 412 of the second recording reproductionsurface 41, in the irradiation direction of an optical beam 81, that is,seen from above the surface. In addition, a length of the area Δ1 andthat of the area Δ2 are equal to L1−G1.

Furthermore, the optical beam 81 passes through the area Δ1 of the firstrecording reproduction surface 31 and is emitted onto the area Δ2 of thesecond recording reproduction surface 41 to record information.

Here, when the two recording reproduction surfaces of this multilayeroptical disc are made of phase change type recording reproduction films,a recording in a phase change type recording reproduction film isperformed based on the principle of changing its crystal structure byirradiation of a high-power optical beam. Therefore, when the recordingis preformed for the area Δ2 in the second recording reproductionsurface 41, that is, for the area at the front end portion in the dataarea 412 of the second recording reproduction surface 41, the high-poweroptical beam 81 is emitted also onto the area Δ1 at the rear end portionin the address area 311 of the first recording reproduction surface 31.

Therefore, the crystal structure of the recording reproduction filmformed on one part in the address area 311 of the first recordingreproduction surface 31 also is affected. As a result, when the addressarea 311 of the first recording reproduction surface 31 is to bereproduced after completing the recording operation for the secondrecording reproduction surface 41, the S/N ratio of the reproducedsignal is deteriorated, and the problem that the address informationcannot be recognized correctly arises.

Furthermore, the example shown in FIG. 8 was explained by referring tothe case where the first recording reproduction surface 31 and thesecond recording reproduction surface 41 were bonded together in a statein which the front position in the sector of the first recordingreproduction surface 31 is shifted to the right side of the surfacerelative to the second recording reproduction surface 41. Similarly,also in the case where the front position in the sector of the firstrecording reproduction surface 31 is shifted to the left side of thesurface relative to the second recording reproduction surface 41 andbonded together, the address area 411 of the second recordingreproduction surface 41 is affected when a recording operation for thefirst recording reproduction surface 31 is performed. As a result, theS/N ratio of the reproduced signal from the address area 411 isdeteriorated, and the problem that the address information cannot berecognized correctly arises.

Moreover, the conventional example was explained by referring to thecase of having two recording reproduction surfaces, but also in the caseof having three and more recording reproduction surfaces, a recordingoperation for an arbitrary recording reproduction surface affectsaddress areas in other recording reproduction surfaces, so that theproblem that this address information cannot be recognized correctlyarises.

Furthermore, in the case where data are already recorded in the dataareas of both recording reproduction surfaces, at the time when arecording operation is performed for one of the recording reproductionsurfaces, also for the data area in the other recording reproductionsurface, a high-power optical beam is emitted onto an area where therespective data areas overlap with each other (Δ3 shown in FIG. 8), sothat errors arise due to the deteriorated S/N ratio of the reproducedsignal. Generally, an error correction code is appended to data, so thatthe content of the reproduced data is restored by this function to somedegree but not completely. The deterioration in the S/N ratio of thereproduced signal in this data area will be explained below more indetail.

Like FIG. 8, FIG. 10 is a diagram expressing the actual sector structureof a conventional multilayer optical disc in the form of a schematicsector structure for each recording reproduction surface. In addition,in FIG. 10, the same reference numerals are given to the sameconstituents as those in FIG. 8, and the explanations thereof areomitted.

First, FIG. 10(a) will be explained. FIG. 10(a) shows a state in whichthe first recording reproduction surface 31 is shifted in the scanningdirection (to the right side of the surface) of the optical beam 81relative to the second recording reproduction surface 41 and bondedtogether. In FIG. 10, a section Z1 or a section Z3 is an area where thedata area 312 of the first recording reproduction surface 31 does notoverlap with the data area 412 of the second recording reproductionsurface 41 and corresponds to a predetermined precision at the time whenthe two recording reproduction surfaces are bonded together. Moreover, asection Z2 shows an area where the data area 312 of the first recordingreproduction surface 31 overlaps with the data area 412 of the secondrecording reproduction surface 41.

When optical information (data) is already recorded in the data area 312of the first recording reproduction surface 31, due to the fact that theoptical conditions of the recording reproduction surfaces differ andthat the transmittances of the optical beam 81 are different, therecording power of the emitted optical beam 81 differs in the section Z1and in the section Z2 of the data area 412 on the second recordingreproduction surface 41.

Next, FIG. 10(b) will be explained. FIG. 10(b) shows a state in whichthe first recording reproduction surface 31 is shifted in the directionopposite to the scanning direction (to the left side of the surface) ofthe optical beam 81 relative to the second recording reproductionsurface 41 and bonded together. As in FIG. 10(a), the section Z1 or thesection Z3 shown in FIG. 10(b) is an area where the data area 312 of thefirst recording reproduction surface 31 does not overlap with the dataarea 412 of the second recording reproduction surface 41 and correspondsto a predetermined precision at the time when the two recordingreproduction surfaces are bonded together. Moreover, as in FIG. 10(a),also the section Z2 shows an area where the data area 312 of the firstrecording reproduction surface 31 overlaps with the data area 412 of thesecond recording reproduction surface 41.

Here, when data are already recorded in the data area 312 of the firstrecording reproduction surface 31, due to the fact that the opticalconditions of the recording reproduction surfaces differ and that thetransmittances of the optical beam 81 are different, the recording powerof the emitted optical beam 81 differs in the section Z1 and in thesection Z2 of the data area 412 on the second recording reproductionsurface 41.

When the transmittance before recording is smaller than thetransmittance after recording, a recording for the second recordingreproduction surface 41 is performed by taking this transmittance intoaccount. But even when the data could be recorded with an optimalrecording power in the section Z2, a recording beam with an excessivepower is emitted onto the portion corresponding to the section Z1 (inthe case of FIG. 10(a)) or the section Z3 (in the case of FIG. 10(b)).On the other hand, when the transmittance before recording is largerthan the transmittance after recording, a recording for the secondrecording reproduction surface 41 is performed by taking thistransmittance into account. But even when the data could be recordedwith an optimal recording power in the section Z2, a recording beam witha much smaller power will be emitted onto the portion corresponding tothe section Z1 (in the case of FIG. 10(a)) or the section Z3 (in thecase of FIG. 10(b)).

As a result, when a reproduction signal is to be obtained from thesecond recording reproduction surface 41, a difference in the signalamplitude of the reproduction signal may arise between the portionscorresponding to the sections Z1 and Z2 (in the case of FIG. 10(a)) orthe sections Z2 and Z3 (in the case of FIG. 10(b)). Thus, a differencein the S/N ratio may arise within the data area, so that a part of thedata recorded in the second recording reproduction surface 41 may not beread out correctly even by using an error correction code appended tothe data.

In particular, when a phase change type material is used for therecording films constructing the recording reproduction surfaces, due tothe fact that its phase state changes (crystal state and amorphousstate) by recording data, the difference in the transmittance before andafter the recording is large, so that the problem mentioned abovebecomes more notable.

DISCLOSURE OF THE INVENTION

Therefore, it is an object of the present invention to provide amultilayer optical disc capable of reproducing an address signal and adata signal correctly even when using a multilayer optical disc that ismade up of a plurality of recording reproduction surfaces bondedtogether in a state in which front positions in sectors of therespective recording reproduction surfaces do not match completely.Another object is to provide a method and a device for recording opticalinformation in this multilayer optical disc.

To achieve the above object, a first multilayer optical disc of thepresent invention is characterized in that the multilayer optical dischas a plurality of recording reproduction surfaces having a sectorstructure, in which an address area and a data area recorded in advanceare divided by a gap area of a predetermined length, and that theplurality of recording reproduction surfaces are bonded together suchthat front positions of sectors in the plurality of recordingreproduction surfaces are aligned with a precision of not more than thelength of the gap area.

Furthermore, to achieve the above object, a second multilayer opticaldisc of the present invention is characterized in that a plurality ofrecording reproduction surfaces having a sector structure, in which anaddress area and a data area recorded in advance are divided by a gaparea, are bonded together with a predetermined precision with referenceto front positions of the sectors, and that the length of the gap areais not less than the predetermined precision with reference to the frontpositions of the sectors.

Furthermore, to achieve the above object, a third multilayer opticaldisc of the present invention is characterized in that the multilayeroptical disc includes a first recording surface and a second recordingsurface, each having an address area, a data area for recordinginformation and a gap area with a predetermined length arranged betweenthe address area and the data area, wherein an amount of displacementbetween a front position in the address area of the first recordingsurface and a front position in the address area of the second recordingsurface, seen from a direction of a beam emitted onto the recordingsurfaces for recording and reproduction of information, is smaller thanthe length of the gap area.

Furthermore, to achieve the above object, a fourth multilayer opticaldisc of the present invention is characterized in that the multilayeroptical disc includes a first recording surface and a second recordingsurface, each having an address area, a data area for recordinginformation and a gap area with a predetermined length arranged betweenthe address area and the data area, wherein an amount of displacementbetween a back end position in the address area of the first recordingsurface and a back end position in the address area of the secondrecording surface, seen from a direction of a beam emitted onto therecording surfaces for recording and reproduction of information, issmaller than the length of the gap area.

Furthermore, to achieve the above object, an optical informationrecording method according to the present invention is a method forrecording optical information in a multilayer optical disc including aplurality of recording reproduction surfaces formed on every layer, witha sector structure having a gap area arranged between an address areaand a data area in a scanning direction of an optical beam, wherein abonding precision L with reference to a front position in the sector ofa certain recording reproduction surface and a length G of the gap areain the scanning direction satisfies a relationship of L≦G for allrecording reproduction surfaces. The method is characterized by thesteps of detecting an amount of displacement between front positions inthe sectors of other recording reproduction surfaces relative to thefront position in the sector of the certain recording reproductionsurface, and, based on the detected amount of displacement, determininga data recording starting position and a data recording ending positionfor each recording reproduction surface such that the data recordingstarting position and the data recording ending position of therespective sectors are matched in the plurality of recordingreproduction surfaces.

In addition, in the optical information recording method of the presentinvention, it is preferable that the data recording starting positionand the data recording ending position respectively are determined to bethe starting position and the ending position in the data area of therecording reproduction surface where the front position of the sector isdisplaced most in a direction opposite to the scanning direction amongthe plurality of recording reproduction surfaces.

Furthermore, to achieve the above object, an optical informationrecording device according to the present invention is a method forrecording optical information in a multilayer optical disc including aplurality of recording reproduction surfaces formed on every layer, witha sector structure having a gap area arranged between an address areaand a data area in a scanning direction of an optical beam, wherein abonding precision L with reference to a front position in the sector ofa certain recording reproduction surface and a length G of the gap areain the scanning direction satisfies a relationship of L≦G for allrecording reproduction surfaces. The device is characterized in that thedevice includes a detection part for detecting an amount of displacementbetween front positions in the sectors of other recording reproductionsurfaces relative to the front position in the sector of the certainrecording reproduction surface, and a gate signal generation part forgenerating a gate signal designating a data recording ending positionfrom a data recording starting position for each recording reproductionsurface to match the data recording starting positions and the datarecording ending positions of the respective sectors in the plurality ofrecording reproduction surfaces, based on the amount of displacementdetected by the detection part.

In addition, in the optical information recording device of the presentinvention, it is preferable that the gate signal designates the datarecording starting position and the data recording ending position to bethe starting position and the ending position in the data area of therecording reproduction surface where the front position of the sector isdisplaced most in a direction opposite to the scanning direction amongthe plurality of recording reproduction surfaces.

Furthermore, to achieve the above object, a fifth multilayer opticaldisc of the present invention is characterized in that the multilayeroptical disc includes layers on which a plurality of recordingreproduction surfaces are formed, with a sector structure having a gaparea arranged between an address area and a data area in a scanningdirection of an optical beam, bonded together such that front positionsin the sectors of the respective recording reproduction surfaces arecontacted closely to each other in the scanning direction by apredetermined precision, wherein guard data recording areas having alength of not less than the predetermined precision are allocated to atip portion and to a back end portion of the data area in the scanningdirection.

According to the configuration mentioned above, by determining thebonding precision between the plurality of recording reproductionsurfaces to be not more than the predetermined length of the gap area orby determining the length of the gap area to be not less than thebonding precision between the plurality of recording reproductionsurfaces of the multilayer optical disc, a recording operation for anarbitrary recording reproduction surface does not affect address areasin other recording reproduction surfaces, so that the addressinformation can be recognized correctly after completing the recordingat the time of reproduction.

Moreover, even when the plurality of recording reproduction surfaces arebonded together in a state in which they are not matched but shifted, bysatisfying the relationship of L≦G between the predetermined precision Lcorresponding to this amount of displacement and the length G of the gaparea, matching the recording range for a certain recording reproductionsurface with the data area, determining the recording range for otherrecording reproduction surfaces to be an area including a part of thegap area in addition to the most part of the data area, and recordingwhile matching the data recording starting positions and the datarecording ending positions in the plurality of recording reproductionsurfaces, even in the case where the certain recording reproductionsurface is already recorded, the recording for the other recordingreproduction surfaces can be performed with a uniform recording power.Therefore, a non-uniform recording power can be prevented, and anamplitude difference in the reproduction signal of the data, that is, aS/N difference is suppressed, so that the recorded data information canbe reproduced correctly.

Furthermore, even when the respective data areas in the plurality ofrecording reproduction surfaces have portions overlapping in thescanning direction, by providing guard data recording areas for dataprotection in the tip portion and the back end portion of the dataareas, the reproduced data information is not affected even when thereis an amplitude difference in the reproduction signal in these guarddata recording areas resulting from the effective power difference inthe recording beam, and therefore, correct reproduced data informationcan be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a schematic sector structure of eachrecording reproduction surface in a multilayer optical disc according toa first embodiment of the present invention.

FIG. 2 is a diagram showing a schematic sector structure of eachrecording reproduction surface in a multilayer optical disc according toa second embodiment of the present invention.

FIG. 3(a) and FIG. 3(b) are diagrams respectively showing a schematicsector structure of each recording reproduction surface in a multilayeroptical disc for explaining one example of a recording method of amultilayer optical disc according to a third embodiment of the presentinvention, in cases where a first recording reproduction surface isshifted in the scanning direction relative to a second recordingreproduction surface and in the direction opposite to the scanningdirection.

FIG. 4 is a block diagram showing an configuration of a multilayeroptical disc recording device according to a fourth embodiment of thepresent invention.

FIG. 5(a) and FIG. 5(b) are timing charts of major signals in themultilayer optical disc recording device shown in FIG. 4 respectivelycorresponding to a displacement of each recording reproduction surfaceshown in FIG. 3(a) and FIG. 3(b).

FIG. 6(a) and FIG. 6(b) are diagrams respectively showing a schematicsector structure of each recording reproduction surface in a multilayeroptical disc according to a fifth embodiment of the present invention,in cases where a first recording reproduction surface is shifted in thescanning direction relative to a second recording reproduction surfaceand in the direction opposite to the scanning direction.

FIG. 7 is a cross-sectional view showing a conventional multilayeroptical disc taken in the direction perpendicular to the trackingdirection.

FIG. 8 is a diagram showing a schematic sector structure of eachrecording reproduction surface in a conventional multilayer opticaldisc.

FIG. 9(a) and FIG. 9(b) respectively are a plan view of a multilayeroptical disc and an enlarged view of a vicinity of an address area in atrack.

FIG. 10(a) and FIG. 10(b) are diagrams respectively showing a schematicsector structure of each recording reproduction surface in aconventional multilayer optical disc, in cases where a first recordingreproduction surface is shifted in the scanning direction relative to asecond recording reproduction surface and in the direction opposite tothe scanning direction.

BEST MODE FOR CARRYING OUT THE INVENTION

In the following, preferable embodiments of the present invention willbe explained by referring to the drawings. Here, for the purposes ofsimplicity, a multilayer optical disc having a double layer structurewill be used for explanation.

First Embodiment

FIG. 1 shows the sector structure of each recording reproduction surfacein a multilayer optical disc according to a first Embodiment of thepresent invention, which is expressed in the form of a schematic sectorstructure for clarifying the characteristics of the present invention,as with FIG. 8 showing a conventional example.

In FIG. 1, 32 and 42 respectively are a first recording reproductionsurface and a second recording reproduction surface in the presentembodiment shown in the form of sector formats. Furthermore, 321 and 421respectively are address areas of the first recording reproductionsurface 32 and the second recording reproduction surface 42, and 322 and422 respectively are data areas of the first recording reproductionsurface 32 and the second recording reproduction surface 42. 323 and 423respectively are gap areas with a predetermined length in the firstrecording reproduction surface 32 and the second recording reproductionsurface 42, both of which are G2 in length.

Furthermore, L2 shows an amount of displacement between front positionsin sectors of the respective recording reproduction surfaces at the timewhen the first recording reproduction surface 32 and the secondrecording reproduction surface 42 are bonded together. This amount ofdisplacement L2 satisfies the relationship L2≦G2, where G2 is the lengthof the gap areas 323 and 324. Thus no overlapping area exists whenviewed from above the surface in the irradiation direction of an opticalbeam 81, such as can be seen in FIG. 8 at the back end of the addressarea 321 of the first recording reproduction surface 32 and at the frontend of the data area 422 of the second recording reproduction surface42. The tolerance in the amount of displacement L2 where no overlappingarea exists corresponds to the length G2 of the gap area 323 and 423. Inother words, when the bonding precision L2 between the front positionsof the sectors is determined to be not more than the length G2 of thegap area, an overlapping area does not exist any more.

Therefore, according to FIG. 1, when a recording for the secondrecording reproduction surface 42 is performed, a high-power opticalbeam 82 is emitted from the front in the data area 422 of the secondrecording reproduction surface 42, and at this time, an area of thefirst recording reproduction surface 32 on which the high-power opticalbeam 82 is emitted is its gap area 323. Thus, a high-power irradiationto the address area 321 of the first recording reproduction surface 32can be avoided, and the crystal structure of a recording reproductionfilm formed in the address area 321 is not affected. As a result, evenwhen the address area 321 of the first recording reproduction surface 32is reproduced after the recording operation for the second recordingreproduction surface 42 is completed, the S/N ratio of the reproducedsignal is not deteriorated, and the address information can berecognized correctly.

Furthermore, as shown in FIG. 1, the present embodiment was explained byreferring to the case in which the first recording reproduction surface32 and the second recording reproduction surface 42 are bonded togetherin a state in which the front position in the sector of the firstrecording reproduction surface 32 is shifted to the right side of thesurface relative to the second recording reproduction surface 42.However, also in the case in which the front position in the sector ofthe first recording reproduction surface 32 is shifted to the left sideof the surface relative to the second recording reproduction surface 42and bonded together, when a recording operation for the first recordingreproduction surface 32 is performed, the high-power optical beam 82 isemitted from the front in the data area 322 of the first recordingreproduction surface 32, and at this time, an area of the secondrecording reproduction surface 42 on which the high-power optical beam82 is emitted is its gap area 423.

Therefore, a high-power irradiation to the address area 421 of thesecond recording reproduction surface 42 can be avoided, and the crystalstructure of a recording reproduction film formed in the address area421 is not affected. As a result, even when the address area 421 of thesecond recording reproduction surface 42 is reproduced after therecording operation for the first recording reproduction surface 32 iscompleted, the S/N ratio of the reproduced signal is not deteriorated,and the address information can be recognized correctly.

Furthermore, the present embodiment was explained by referring to thecase of having two recording reproduction surfaces. However, it isneedless to say that even when there are three or more recordingreproduction surfaces, a recording operation for an arbitrary recordingreproduction surface does not affect address areas in other recordingreproduction surfaces, and that the address information can berecognized correctly.

In this way, by bonding together the plurality of recording reproductionsurfaces such that the amount of displacement between the frontpositions of the sectors in the plurality of recording reproductionsurfaces, that is, the bonding precision for the plurality of recordingreproduction surfaces, is not more than the predetermined length of thegap area, the address information can be recognized correctly when it isreproduced after recording.

Second Embodiment

FIG. 2 shows the sector structure of each recording reproduction surfacein a multilayer optical disc according to a second Embodiment of thepresent invention, which is expressed in the form of a schematic sectorstructure for clarifying the characteristics of the present invention,as in the first Embodiment.

In FIG. 2, 33 and 43 are a first recording reproduction surface and asecond recording reproduction surface in the present embodiment shown inthe form of sector formats. Furthermore, 331 and 431 respectively areaddress areas of the first recording reproduction surface 33 and thesecond recording reproduction surface 43, and 332 and 432 respectivelyare data areas of the first recording reproduction surface 33 and thesecond recording reproduction surface 43. 333 and 433 respectively aregap areas of the first recording reproduction surface 33 and the secondrecording reproduction surface 43.

Furthermore, L3 shows an amount of displacement between front positionsin sectors of the respective recording reproduction surfaces at the timewhen the first recording reproduction surface 33 and the secondrecording reproduction surface 43 are bonded together. This amount ofdisplacement L3 shows a threshold value of this bonding precision, thatis, a maximum amount of displacement with reference to the frontpositions of the sectors when the first recording reproduction surface33 and the second recording reproduction surface 43 are bonded together.

Therefore, it satisfies L3≦G3, where G3 is the length of the gap areas333 and 433. Thus no overlapping area exists when viewed from above thesurface in the irradiation direction of an optical beam, such as can beseen in FIG. 8 at the back end of the address area 331 of the firstrecording reproduction surface 33 and at the front end of the data area432 of the second recording reproduction surface 43. To eliminate thisoverlapping area, the length G3 of the gap area should be determined tobe not less than the threshold value L3 of the bonding precision betweenthe respective recording reproduction surfaces.

Therefore, according to FIG. 2, when a recording for the secondrecording reproduction surface 43 is performed, a high-power opticalbeam 83 is emitted from the front in the data area 432 of the secondrecording reproduction surface 43, and at this time, an area of thefirst recording reproduction surface 33 on which the high-power opticalbeam 83 is emitted is its gap area 333. Thus, a high-power irradiationto the address area 331 of the first recording reproduction surface 33can be avoided, and the crystal structure of a recording reproductionfilm formed in the address area 331 is not affected. As a result, evenwhen the address area 331 of the first recording reproduction surface 33is reproduced after the recording operation for the second recordingreproduction surface 43 is completed, the S/N ratio of the reproducedsignal is not deteriorated, and the address information can berecognized correctly.

Furthermore, as shown in FIG. 2, the present embodiment was explained byreferring to the case in which the first recording reproduction surface33 and the second recording reproduction surface 43 are bonded togetherin a state in which the front position in the sector of the firstrecording reproduction surface 33 is shifted to the right side of thesurface relative to the second recording reproduction surface 43.However, also in the case in which the front position in the sector ofthe first recording reproduction surface 33 is shifted to the left sideof the surface relative to the second recording reproduction surface 43and bonded together, when a recording operation for the first recordingreproduction surface 33 is performed, the high-power optical beam 83 isemitted from the front in the data area 332 of the first recordingreproduction surface 33, and at this time, an area of the secondrecording reproduction surface 43 on which the high-power optical beam83 is emitted is its gap area 433.

Therefore, a high-power irradiation on the address area 431 of thesecond recording reproduction surface 43 can be avoided, and the crystalstructure of a recording reproduction film formed in the address area431 is not affected. As a result, even when the address area 431 of thesecond recording reproduction surface 43 is reproduced after therecording operation for the first recording reproduction surface 33 iscompleted, the S/N ratio of the reproduced signal is not deteriorated,and the address information can be recognized correctly.

Furthermore, the present embodiment was explained by referring to thecase of having two recording reproduction surfaces. However, the featureof the present invention is applicable also to the case of having threeor more recording reproduction surfaces. According to the presentinvention, a recording operation for an arbitrary recording reproductionsurface does not affect address areas in other recording reproductionsurfaces, and its address information can be recognized correctly.

In this way, by securing the length of the gap area to be not less thanthe threshold value of the bonding precision for the plurality ofrecording reproduction surfaces, the address information can berecognized correctly when it is reproduced after recording, and the sameeffect as that shown in the first Embodiment can be obtained.

Furthermore, the first Embodiment and the second Embodiment arecharacterized in that the amount of displacement between the frontpositions of the sectors is not more than the length of the gap area,and also in that the amount of displacement between the back ends of theaddress areas is not more than the length of the gap area.

Third Embodiment

FIG. 3(a) and FIG. 3(b) are diagrams showing the actual sector structureof each recording reproduction surface in a multilayer optical discaccording to a third Embodiment of the present invention, which isexpressed in the form of a schematic sector structure. FIG. 3(a) shows astate in which a first recording reproduction surface 34 is shifted inthe scanning direction (to the right side of the drawing) of an opticalbeam 84 relative to a second recording reproduction surface 44 andbonded together. Furthermore, FIG. 3(b) shows a state in which the firstrecording reproduction surface 34 is shifted in the direction oppositeto the scanning direction (to the left side of the drawing) of theoptical beam 84 relative to the second recording reproduction surface 44and bonded together.

In FIG. 3(a) and FIG. 3(b), 341, 343 and 342 respectively show anaddress area, a gap area and a data area of the first recordingreproduction surface 34, and 441, 443 and 442 respectively show anaddress area, a gap area and a data area of the second recordingreproduction surface 44. In addition, 341 and 441, 343 and 443, and 342and 442 respectively have an equal length in the scanning direction ofthe optical beam 84. Furthermore, a section Z1 shows a section in FIG.3(a) where a tip portion in the data area 442 of the second recordingreproduction surface 44 overlaps with the gap area 343 of the firstrecording reproduction surface 34 and also a section in FIG. 3(b) wherea tip portion in the data area 342 of the first recording reproductionsurface 34 overlaps with the gap area 443 of the second recordingreproduction surface 44. Therefore, a section Z2 shows a section wherethe data area 342 of the first recording reproduction surface 34overlaps with the data area 442 of the second recording reproductionsurface 44, and the section Z1 corresponds to a bonding precisionbetween the first recording reproduction surface 34 and the secondrecording surface 44. Furthermore, the section Z1 is configured so as tobe not more than the length of the gap area 343 of the first recordingreproduction surface 34 and the gap area 443 of the second recordingreproduction surface 44.

Furthermore, in FIG. 3(a), an area X1 shown by oblique lines on thefirst recording reproduction surface 34 shows a recording range forrecording information in the first recording reproduction surface 34.That is, the recording range X1 for recording information in the firstrecording reproduction surface 34 corresponds to the total rangeobtained by adding the section Z1 at the back end portion in the gaparea 343 of the first recording reproduction surface 34 and the sectionZ2.

In this way, by determining the recording range for recordinginformation in the first recording reproduction surface 34 to be thesame as the data area 442 of the recording range for recordinginformation in the second recording reproduction surface 44, therecording ranges of the first recording reproduction surface 34 and thesecond recording reproduction surface 44 are matched. In other words,the data recording starting positions and the data recording endingpositions are matched on the two recording reproduction surfaces.

The amount of information to be recorded is the same for the tworecording reproduction surfaces. This amount of information becomesequal to the amount of information predetermined by the data areas 342and 442.

On the other hand, in FIG. 3(b), an area X2 shown by oblique lines onthe second recording reproduction surface 44 shows a recording range forrecording information in the second recording reproduction surface 44.That is, the recording range X2 for recording information in the secondrecording reproduction surface 44 corresponds to the total rangeobtained by adding the section Z1 at the back end portion in the gaparea 443 of the second recording reproduction surface 44 and the sectionZ2.

In this way, by determining the recording range for recordinginformation in the second recording reproduction surface 44 to be thesame as the data area 342 of the recording range for recordinginformation in the first recording reproduction surface 34, therecording ranges of the first recording reproduction surface 34 and thesecond recording reproduction surface 44 are matched. In other words,the data recording starting positions and the data recording endingpositions are matched on the two recording reproduction surfaces. Alsoin this case, the amount of information to be recorded is the same forthe two recording reproduction surfaces, and this amount of informationbecomes equal to the amount of information predetermined by the dataareas 342 and 442.

In this way, even when the two recording reproduction surfaces arebonded together in a state in which they are not matched but shifted, bysatisfying the relationship of L≦G between the predetermined precision Lcorresponding to this amount of displacement (the length of the sectionZ1 in FIG. 3(a) and FIG. 3(b)) and the length G of the gap areas 343 and443, matching the recording range for one of the recording reproductionsurfaces with the data area (442 in FIG. 3(a) and 342 in FIG. 3(b)),determining the recording range for the other recording reproductionsurface to be an area including a part of the gap area in addition tothe most part of the data area (X1 in FIG. 3(a) and X2 in FIG. 3(b)),and recording while matching the recording ranges of the two recordingreproduction surfaces, that is, the data recording starting positionsand the data recording ending positions, the recording for the secondrecording reproduction surface can be performed with a uniform recordingpower even when the first recording reproduction surface is alreadyrecorded. Therefore, such a non-uniform recording power as thatdescribed in the conventional example can be prevented, and an amplitudedifference in the reproduction signal also can be suppressed. As aresult, the recorded data information can be reproduced correctly.

In addition, the amount of information to be recorded in the tworecording reproduction surfaces is not reduced from the amountpredetermined for the data area of each recording reproduction surface.Moreover, when the bonding precision between the two recordingreproduction surfaces is determined to be not more than the length ofthe gap area located between the address area and the data area, even ifthe recording starting positions of the two recording reproductionsurfaces are matched, neither of the recording starting positions of therecording reproduction surfaces breaks into the address area of thisrecording reproduction surface. Therefore, the reproduction signal inthe address area also is not affected.

As explained above, the recording method of a multilayer optical discaccording to the present embodiment neither affects the amount ofinformation to be recorded nor the reproduction signal in the addressarea and enables recording of optical information with a uniformrecording power.

In addition, as described above, when two recording reproductionsurfaces are provided, it is preferable to match the range for recordingdata with either one of the data areas of the recording reproductionsurfaces.

Fourth Embodiment

A fourth embodiment relates to an information recording reproductiondevice for recording information in the multilayer optical discdescribed in the third embodiment.

In the following, an information recording reproduction device in thepresent embodiment will be explained by referring to the drawing. Sincethe intended multilayer optical disc was explained in the thirdembodiment, FIG. 3(a) and FIG. 3(b) will be referred to from time totime in the description.

FIG. 4 is a block diagram showing an information recording reproductiondevice according to a fourth embodiment of the present invention. InFIG. 4, 101 is a reproduction beam, and 102 is a recording beam. Byusing the reproduction beam 101 or the recording beam 102 via anobjective lens 122, a signal is reproduced from or information isrecorded in a multilayer optical disc 100 (having a double layerstructure shown in FIG. 3(a) and FIG. 3(b)), which is rotating at a ratefor obtaining a predetermined linear velocity. Furthermore, 150 is amotor for rotating the multilayer optical disc 100, and 151 is a rotaryencoder attached to the motor for sending one pulse 152 per onerotation.

Furthermore, 104 is a photoelectric converter used for obtaining areproduction signal 105 from the reproduction beam 101 as an electricsignal. The reproduction signal 105 is input into an address signalreproduction processing part 106 (a part surrounded by the dotted linein FIG. 4) and processed therein by an envelope detector 107, acomparator 109 and an edge detector 110, and a reset signal 115 for acounter 123 is sent from the address signal reproduction processing part106. On the other hand, in the counter 123, a clock 111 is input in itsclock input terminal, and set values P and Q are input into their datainput terminals.

When a recording operation is performed for the first recordingreproduction surface 34 shown in FIG. 3(a) and FIG. 3(b), set values P1and Q1 become the set values P and Q to be set for the counter 123 via aselect circuit 130. On the other hand, when a recording operation isperformed for the second recording reproduction surface 44, set valuesP2 and Q2 become the set values P and Q to be set for the counter 123via the select circuit 130. Furthermore, the select circuit 130 iscontrolled by the state of a control command 131, and the state of thecontrol command 131 is determined by whether the recording operation isperformed for the first recording reproduction surface 34 or therecording operation is performed for the second recording surface 44.

Moreover, the counter 123 outputs a set input signal 119 of a flip-flop124 after a first predetermined time, determined by the set value P andthe frequency of the clock 111, has passed from the time when the resetsignal 115 was activated. Furthermore, the counter 123 outputs a resetinput signal 120 of the flip-flop 124 after a second predetermined time,determined by the set value Q and the frequency of the clock 111, haspassed from the above time. Therefore, the first predetermined time andthe second predetermined time respectively are different times when therecording for the first recording reproduction surface 34 and that forthe second recording reproduction surface 44 are performed.

Furthermore, by controlling a switch 112 by an output signal 121 fromthe flip-flop 124, the supply of recording data 113 to an opticalmodulator 103 can be controlled, and a recording signal 125 can beobtained. Moreover, the recording beam 102 is obtained from therecording signal 125 through the function of the optical modulator 103,and this recording beam 102 is emitted onto the multilayer optical disc100 via the objective lens 122 to record the desired data.

In this way, the counter 123, the set values P, Q thereof and theflip-flop 124 construct a recording gate generation part for generatingrecording gate signals.

Next, the operation of the information recording reproduction deviceaccording to the embodiment of the above configuration will be explainedfirst referring to FIG. 5(a) showing the timing of its major signal.

FIG. 5(a) shows the process of generating a timing for determining theoperation at the time when a recording is performed for the multilayeroptical disc shown in FIG. 3(a), in which the first recordingreproduction surface 34 is bonded together with the bonding precision Z1and in the state in which the first recording reproduction surface 34 isshifted to the right side of the surface relative to the secondrecording reproduction surface 44 (in addition, in FIG. 3(a), theoptical beam 84 emitted as a recording beam from above the surfacebecomes a reproduction beam at the time of reproduction).

In FIG. 5(a), 105 a, 116 a, 117 a and 115 a respectively correspond tothe reproduction signal 105 when the first recording reproductionsurface 34 is reproduced (only the address reproduction signal from theaddress area is shown), an output signal 116 of the envelope detector107, an output signal 117 of the comparator 109 and the output signal115 of the edge detector 110 (the reset signal of the counter 123).Moreover, 119 a and 120 a respectively correspond to the set signal 119and the reset signal 120 sent to the flip-flop 124 when the set values Pand Q for the counter 123 respectively became P1 and Q1 by the selectcircuit 130, that is, when the recording for the first recordingreproduction surface 34 is to be performed, and 121 a corresponds to theoutput signal 121 of the flip-flop 124 (the control signal of the switch112). Furthermore, T1 a is a period from the time when 115 a isactivated to the time when 119 a is activated, which corresponds to thefirst predetermined time mentioned above, and T2 a is a period from thetime when 119 a is activated to the time when 120 a is activated, whichcorresponds to the second predetermined time mentioned above.

Furthermore, T2 a is equal to the period during which the output signal121 of the flip-flop 124 (the control signal of the switch 112), thatis, 121 a is activated, and therefore, 125 a is the timing of therecording signal 125 with which the recording data 113 is gated by theswitch 112.

Furthermore, 105 b, 116 b, 117 b and 115 b respectively correspond tothe reproduction signal 105 when the second recording reproductionsurface 44 is reproduced (only the address reproduction signal isshown), the output signal 116 of the envelope detector 107, the outputsignal 117 of the comparator 109 and the output signal 115 of the edgedetector 110 (the reset signal of the counter 123). Moreover, 119 b and120 b respectively correspond to the set signal 119 and the reset signal120 sent to the flip-flop 124 when the set values P and Q for thecounter 123 respectively became P2 and Q2 by the select circuit 130,that is, when the recording for the second recording reproductionsurface 44 is performed, and 121 b corresponds to the output signal 121of the flip-flop 124 (the control signal of the switch 112).Furthermore, T1 b is a period from the time when 115 b is activated tothe time when 119 b is activated, which corresponds to the firstpredetermined time mentioned above, and T2 b is a period from the timewhen 119 b is activated to the time when 120 b is activated, whichcorresponds to the second predetermined time mentioned above.

Furthermore, T2 b is equal to the period during which the output signal121 of the flip-flop 124 (the control signal of the switch 112), thatis, 121 b is activated, and therefore, 125 b is the timing of therecording signal 125 with which the recording data 113 is gated by theswitch 112.

Therefore, T1 a and T1 a+T2 a respectively are determined by the setvalues P1, Q1 and the clock frequency of the counter 123, and T1 b andT1 b+T2 b respectively are determined by the set values P2, Q2 and theclock frequency of the counter 123. T1 a and T1 b, T1 a+T2 and T1 b+T2 brespectively are different times.

Thus, in the case where the first recording reproduction surface 34 andthe second recording reproduction surface 44 of the object multilayeroptical disc 100 are bonded together as shown in FIG. 3(a), and themultilayer optical disc 100 is rotating at a predetermined linearvelocity V, at the time when the recording for the first recordingreproduction surface 34 is performed, the set value P1 is determinedsuch that the value of T1 a becomes equal to (A2+G2−Z1)/V (here, A2 andG2 respectively show the length of the address area 341 and the lengthof the gap area 343 on the first recording reproduction surface 34), andthe set value Q1 is determined such that the value of T1 a+T2 a becomesequal to (A2+G2+Z2)/V. Then, the state of the control input 131 for theselect circuit 130 is determined such that these values become the setvalues for the counter 123.

On the other hand, at the time when the recording for the secondrecording reproduction surface 44 is performed, the set value P2 isdetermined such that the value of T1 b becomes equal to (A3+G3)/V (here,A3 and G3 respectively show the length of the address area 441 and thelength of the gap area 443 on the second recording reproduction surface44), and the set value Q2 is determined such that the value of T1 b+T2 bbecomes equal to (A3+G3+Z1+Z2)/V, that is, (A3+G3+D3)/V (here, D3 showsthe length of the data area 442 on the second recording reproductionsurface 44). Then, as mentioned above, the state of the control input131 for the select circuit 130 is determined such that these valuesbecome the set values for the counter 123.

In this way, while the recording signal 125 a for the first recordingreproduction surface 34 and the recording signal 125 b for the secondrecording reproduction surface 44 are activated, both T2 a and T2 b havethe same timing, so that the data recording starting positions and thedata recording ending positions are matched on the first recordingreproduction surface 34 and the second recording reproduction surface34. That is, the recording ranges become the section X1 of the firstrecording reproduction surface 34 shown in FIG. 3(a) and the data area442 of the second recording reproduction surface 44, so that therecording ranges are matched.

In other words, when the recording for the first recording reproductionsurface 34 is performed, the recording starting position thereof isadvanced from the front of the data area 342 by the bonding precision Z1between the two recording reproduction surfaces (i.e. shifted to thedirection opposite to the scanning direction), and the recording endingposition is set to be the back end of the area Z2 where the data area342 of the first recording reproduction surface 34 overlaps with thedata area 442 of the second recording reproduction surface 44. When therecording for the second recording reproduction surface 44 is performed,by determining the predetermined data area 442 as the recording range,the data recording starting positions and the data recording endingpositions on the two recording reproduction surfaces are matched, thatis, the recording ranges are matched.

Next, the operation of the information recording reproduction deviceaccording to the present embodiment shown in FIG. 4 will be explainedreferring to FIG. 5(b) showing the timing of its major signal.

FIG. 5(b) shows the process of generating a timing for determining theoperation at the time when a recording is performed for the multilayeroptical disc shown in FIG. 3(b), in which the first recordingreproduction surface 34 is bonded together with the bonding precision Z1and in the state in which the first recording reproduction surface 34 isshifted to the right side of the surface relative to the secondrecording reproduction surface 44 (in addition, in FIG. 3(b), theoptical beam 84 emitted as a recording beam from above the surfacebecomes a reproduction beam at the time of reproduction).

In FIG. 5(b), 105 a, 116 a, 117 a and 115 a respectively correspond tothe reproduction signal 105 when the first recording reproductionsurface 34 is reproduced (only the address reproduction signal from theaddress area is shown), an output signal 116 of the envelope detector107, an output signal 117 of the comparator 109 and the output signal115 of the edge detector 110 (the reset signal of the counter 123).Moreover, 119 a and 120 a respectively correspond to the set signal 119and the reset signal 120 sent to the flip-flop 124 when the set values Pand Q for the counter 123 respectively became P1 and Q1 by the selectcircuit 130, that is, when the recording for the first recordingreproduction surface 34 is to be performed, and 121 a corresponds to theoutput signal 121 of the flip-flop 124 (the control signal of the switch112). Furthermore, T1 a is a period from the time when 115 a isactivated to the time when 119 a is activated, which corresponds to thefirst predetermined time mentioned above, and T2 a is a period from thetime when 119 a is activated to the time when 120 a is activated, whichcorresponds to the second predetermined time mentioned above.

Furthermore, T2 a is equal to the period during which the output signal121 of the flip-flop 124 (the control signal of the switch 112), thatis, 121 a is activated, and therefore, 125 a is the timing of therecording signal 125 with which the recording data 113 is gated by theswitch 112.

Furthermore, 105 b, 116 b, 117 b and 115 b respectively correspond tothe reproduction signal 105 when the second recording reproductionsurface 44 is reproduced (only the address reproduction signal isshown), the output signal 116 of the envelope detector 107, the outputsignal 117 of the comparator 109 and the output signal 115 of the edgedetector 110 (the reset signal of the counter 123). Moreover, 119 b and120 b respectively correspond to the set signal 119 and the reset signal120 sent to the flip-flop 124 when the set values P and Q for thecounter 123 respectively became P2 and Q2 by the select circuit 130,that is, when the recording for the second recording reproductionsurface 44 is performed, and 121 b corresponds to the output signal 121of the flip-flop 124 (the control signal of the switch 112).Furthermore, T1 b is a period from the time when 115 b is activated tothe time when 119 b is activated, which corresponds to the firstpredetermined time mentioned above, and T2 b is a period from the timewhen 119 b is activated to the time when 120 b is activated, whichcorresponds to the second predetermined time mentioned above.

Furthermore, T2 b is equal to the period during which the output signal121 of the flip-flop 124 (the control signal of the switch 112), thatis, 121 b is activated, and therefore, 125 b is the timing of therecording signal 125 with which the recording data 113 is gated by theswitch 112.

Therefore, T1 a and T1 a+T2 a respectively are determined by the setvalues P1, Q1 and the clock frequency of the counter 123, and T1 b andT1 b+T2 b respectively are determined by the set values P2, Q2 and theclock frequency of the counter 123. T1 a and T1 b, T1 a+T2 and T1 b+T2 brespectively are different times.

Thus, in the case where the first recording reproduction surface 34 andthe second recording reproduction surface 44 of the object multilayeroptical disc 100 are bonded together as shown in FIG. 3(b), and themultilayer optical disc 100 is rotating at a predetermined linearvelocity V, at the time when the recording for the first recordingreproduction surface 34 is performed, the set value P1 is determinedsuch that the value of T1 a becomes equal to (A2+G2)/V, and the setvalue Q1 is determined such that the value of T1 a+T2 a becomes equal to(A2+G2+D2)/V. Then, the state of the control input 131 for the selectcircuit 130 is determined such that these values become the set valuesfor the counter 123.

On the other hand, at the time when the recording for the secondrecording reproduction surface 44 is performed, the set value P2 isdetermined such that the value of T1 b becomes equal to (A3+G3−Z1)/V(here, A3 and G3 respectively show the length of the address area 441and the length of the gap area 443 on the second recording reproductionsurface 44), and the set value Q2 is determined such that the value ofT1 b+T2 b becomes equal to (A3+G3+Z2)/V. Then, when the state of thecontrol input 131 for the select circuit 130 is determined such thatthese values become the set values for the counter 123, both the timesT2 a and T2 b during which the recording signal 125 a for the firstrecording reproduction surface 34 and the recording signal 125 b for thesecond recording reproduction surface 44 are activated have the sametiming, so that the data recording starting positions and the datarecording ending positions are matched on the first recordingreproduction surface 34 and the second recording reproduction surface34. That is, the recording ranges become the data area 342 of the firstrecording reproduction surface 34 and the section X2 of the secondrecording reproduction surface 34 shown in FIG. 3(b), so that therecording ranges are matched.

In other words, when the recording for the first recording reproductionsurface 34 is performed, the predetermined data area 342 is determinedas the recording range, and when the recording for the second recordingreproduction surface 44 is performed, the data recording startingposition is advanced from the front of the data area 442 by the bondingprecision Z1 between the two recording reproduction surfaces (i.e.shifted to the direction opposite to the scanning direction), and therecording ending position is set to be the back end of the area Z2 wherethe data area 342 of the first recording reproduction surface 34overlaps with the data area 442 of the second recording reproductionsurface 44. Thus, the data recording starting positions and the datarecording ending positions on the two recording reproduction surfacesare matched, that is, the recording ranges are matched.

In addition, the calculation of the bonding precision Z2 between thefirst recording reproduction surface 34 and the second recordingreproduction surface 44 (the detection of the amount of displacement)may be performed as follows. That is, first, from the time when onepulse 152 per one rotation is output from the rotary encoder 151, theoutput time of the output signal 116 from the envelope detector 107 atthe time when the first recording reproduction surface 34 is reproducedis measured. Next, from the time when one pulse 152 per one rotation isoutput from the rotary encoder 151, the output time of the output signal116 from the envelope detector 107 at the time when the second recordingreproduction surface 44 is reproduced is measured. Then, the timedifference between them is calculated and divided by the linear velocityV.

Furthermore, the section Z2 where the data area 342 of the firstrecording reproduction surface 34 overlaps with the data area 442 of thesecond recording reproduction surface 44 can be calculated easily basedon the previously calculated value of Z1, since the lengths of the dataareas on the two recording reproduction surfaces are already known.

In addition, the configuration of the multilayer optical disc used forthe present embodiment is the same as that shown in FIG. 3(a) and FIG.3(b) described in the third embodiment. However, when the place wherethe gap area is to be inserted is located between the data area and theaddress area of the next sector, the data recording starting position ofthe first recording reproduction surface 34 or the second recordingreproduction surface 44 can be delayed by the bonding precision thereofso as to match the data recording starting positions and the datarecording ending positions of the two recording reproduction surfaces,that is, the recording ranges.

As described above, even when the first recording reproduction surface34 and the second recording reproduction surface 44 are bonded togetherin the state in which they are shifted by the predetermined precisionZ1, by determining the recording range of the first recordingreproduction surface 34 and the recording range of the second recordingreproduction surface 44 as mentioned above, even in the case where thefirst recording reproduction surface 34 is already recorded, thetransmittance of the recording beam in the recording range of the secondrecording reproduction surface 44 becomes constant, so that the power ofrecording beam emitted onto this recording range of the second recordingreproduction surface 44 becomes uniform at the time of recording.

Therefore, a difference in the signal amplitude of the reproductionsignal resulting from the non-uniformity of the power of recording beamcan be eliminated within the recorded range, and data can be read outcorrectly from the reproduction signal. In particular, when a phasechange type material is used for the recording films constructing therecording reproduction surfaces, due to the fact that its phase statechanges by recording and that the difference in the transmittance beforeand after the recording is large, more remarkable effect can beobtained.

Fifth Embodiment

FIG. 6(a) and FIG. 6(b) are diagrams showing the actual sector structureof each recording reproduction surface in a multilayer optical discaccording to a fifth Embodiment of the present invention, which isexpressed in the form of a schematic sector structure.

First, it will be explained referring to FIG. 6(a). FIG. 6(a) shows astate in which a first recording reproduction surface 35 is shifted inthe scanning direction (to the right side of the surface) of an opticalbeam 85 relative to a second recording reproduction surface 45 when thefirst recording reproduction surface 35 and the second recordingreproduction surface 45 are bonded together.

In FIG. 6(a), 35 and 45 respectively are the first recordingreproduction surface and the second recording reproduction surface inthe present embodiment shown in the form of sector formats. 351 and 451respectively show address areas of the first recording reproductionsurface 35 and the second recording reproduction surface 45, and 352 and452 respectively show data areas of the first recording reproductionsurface 35 and the second recording reproduction surface 45, 353 and 453respectively show gap areas of the first recording reproduction surface35 and the second recording reproduction surface 45.

Furthermore, 354 and 454 respectively show guard areas (guard dataareas) allocated to tip portions (starting end portions) in the dataareas of the first recording reproduction surface 35 and the secondrecording reproduction surface 45. Furthermore, 355 and 455 respectivelyshow guard areas allocated to back end portions (termination portions)of the first recording reproduction surface 35 and the second recordingreproduction surface 45. The four guard areas mentioned above areprovided to protect the data to be recorded in the data areas, in which,for example, signals having a single frequency are recorded. Moreover,the guard areas 354 and 454, respectively allocated to the tip portionsof the first recording reproduction surface 35 and the second recordingreproduction surface 45, have the equal length L2, and the guard areas355 and 455, respectively allocated to the back end portions of thefirst recording reproduction surface 35 and the second recordingreproduction surface 45, have the equal length L3.

Furthermore, L1 shows an amount of displacement between front positionsin sectors of the respective recording reproduction surfaces at the timewhen the first recording reproduction surface 35 and the secondrecording reproduction surface 45 are bonded together. This amount ofdisplacement L1 is equal to the amount of displacement between the frontpositions in the data areas of the first recording reproduction surface35 and the second recording reproduction surface 45 and shows a bondingprecision between the first recording reproduction surface 35 and thesecond recording reproduction surface 45, which is L1≦L2, compared withthe length L2 of the guard areas 354 and 454.

Here, provided that the data area 352 of the first recordingreproduction surface 35 including the guard data is already recorded,when the recording is performed thereafter for the data area 452 of thesecond recording reproduction surface 45 including the guard data, afluctuation in the effective power of the recording beam is generateddue to the difference in the transmittance of the optical beam 85between the area of the length L1 in the front portion of the data area452 and the residual area. As a result, a difference in the amplitude ofthe reproduction signal arises.

However, the area of the length L1 at the front portion in the data area452 of the second recording reproduction surface 45 is a part of theguard area 454 on the second recording reproduction surface 45, and theguard area is an area provided for the protection of data to be recordedin the data area as mentioned above, so that the reproduction data isnot affected even if the reproduction signal in this area has anamplitude difference resulting from the effective power difference inthe recording beam. Thus, correct reproduction data can be obtained.

In other words, when the bonding precision L1 between the firstrecording reproduction surface 35 and the second recording reproductionsurface 45 is not more than the length L2 of the guard areas 354 and 454respectively allocated to the tip portions in the data areas of thefirst recording reproduction surface 35 and the second recordingreproduction surface 45, the reproduction data is not affected even whenthere is an amplitude difference in the reproduction signal resultingfrom the effective power difference in the recording beam, andtherefore, correct reproduction data can be obtained.

Next, it will be explained referring to FIG. 6(b). FIG. 6(b) shows astate in which the first recording reproduction surface 35 is shifted inthe direction opposite to the scanning direction (to the left side ofthe surface) of the optical beam 85 relative to the second recordingreproduction surface 45 when the first recording reproduction surface 35and the second recording reproduction surface 45 are bonded together.

In FIG. 6(b), as in FIG. 6(a), L1 shows an amount of displacementbetween front positions in sectors of the respective recordingreproduction surfaces at the time when the first recording reproductionsurface 35 and the second recording reproduction surface 45 are bondedtogether. This amount of displacement L1 is equal to the amount ofdisplacement between the back end positions in the data areas of thefirst recording reproduction surface 35 and the second recordingreproduction surface 45 and shows a bonding precision between the firstrecording reproduction surface 35 and the second recording reproductionsurface 45, which is L1≦L3, compared with the length L3 of the guardareas 355 and 455.

Here, provided that the data area 352 of the first recordingreproduction surface 35 including the guard data is already recorded,and when the recording is performed thereafter for the data area 452 ofthe second recording reproduction surface 45 including the guard data, afluctuation in the effective power of the recording beam is generateddue to the difference in the transmittance of the optical beam 85between the area of the length L1 in the back end portion of the dataarea 452 and the residual area, so that a difference in the amplitude ofthe reproduction signal arises.

However, the area of the length L1 at the back end portion in the dataarea 452 of the second recording reproduction surface 45 is a part ofthe guard area 455 on the second recording reproduction surface 45, andthe guard area is an area provided for the protection of data to berecorded in the data area as mentioned above, so that the reproductiondata is not affected even if the reproduction signal in this area has anamplitude difference resulting from the effective power difference inthe recording beam. Thus, correct reproduction data can be obtained.

In other words, when the bonding precision L1 between the firstrecording reproduction surface 35 and the second recording reproductionsurface 45 is not more than the length L3 of the guard areas 355 and 455respectively allocated to the back end portions in the data areas of thefirst recording reproduction surface 35 and the second recordingreproduction surface 45, the reproduction data is not affected even whenthere is an amplitude difference in the reproduction signal resultingfrom the effective power difference in the recording beam, andtherefore, correct reproduction data can be obtained.

As described above, according to the present embodiment, by determiningthe bonding precision between the first recording reproduction surface35 and the second recording reproduction surface 45 to be not more thanthe length of the guard areas 354 and 454 respectively allocated to thetip portions in the data areas of the first recording reproductionsurface 35 and the second recording reproduction surface 45, and also tobe not more than the length of the guard areas 355 and 455 respectivelyallocated to their back end portions, it is possible to perform therecording for obtaining correct reproduction data constantly.

In addition, the present embodiment was explained by referring to thecase of having two recording reproduction surfaces. However, also in thecase of having three or more recording reproduction surfaces, by bondingthe respective recording reproduction surfaces such that the bondingprecision between the recording reproduction surfaces is not more thanthe length of the guard areas allocated to the tip portions of the dataareas and also not more than the length of the guard areas allocated totheir back end portions, it is possible to perform the recording forobtaining correct reproduction data constantly from an arbitraryrecording reproduction surface.

What is claimed is:
 1. A multilayer optical disc comprising a pluralityof recording reproduction surfaces having a sector structure, in whichan address area and a data area recorded in advance are divided by a gaparea of a predetermined length, wherein the plurality of recordingreproduction surfaces are bonded together such that front positions insectors in the plurality of recording reproduction surfaces have aprecision of not more than the length of the gap area.
 2. A multilayeroptical disc comprising a plurality of recording reproduction surfaceshaving a sector structure, in which an address area and a data arearecorded in advance are divided by a gap area, bonded together with apredetermined precision with reference to front positions of thesectors, wherein the length of the gap area is not less than thepredetermined precision with reference to the front positions of thesectors.
 3. A multilayer optical disc comprising a first recordingsurface and a second recording surface, each having an address area, adata area for recording information and a gap area with a predeterminedlength arranged between the address area and the data area, wherein anamount of displacement between a front position in the address area ofthe first recording surface and a front position in the address area ofthe second recording surface, seen from a direction of a beam emittedonto the recording surfaces for recording and reproduction ofinformation, is smaller than the length of the gap area.
 4. A multilayeroptical disc comprising a first recording surface and a second recordingsurface, each having an address area, a data area for recordinginformation and a gap area with a predetermined length arranged betweenthe address area and the data area, wherein an amount of displacementbetween a back end position in the address area of the first recordingsurface and a back end position in the address area of the secondrecording surface, seen from a direction of a beam emitted onto therecording surfaces for recording and reproduction of information, issmaller than the length of the gap area.
 5. An optical informationrecording method for recording optical information in a multilayeroptical disc including a plurality of recording reproduction surfacesformed on every layer, with a sector structure having a gap areaarranged between an address area and a data area in a scanning directionof an optical beam, wherein a bonding precision L with reference to afront position in the sector of a certain recording reproduction surfaceand a length G of the gap area in the scanning direction satisfies arelationship of L≦G for all recording reproduction surfaces, the methodcomprising the steps of detecting an amount of displacement betweenfront positions in the sectors of other recording reproduction surfacesrelative to the front position in the sector of the certain recordingreproduction surface, and, based on the detected amount of displacement,determining a data recording starting position and a data recordingending position for each recording reproduction surface such that thedata recording starting position and the data recording ending positionof the respective sectors are matched in the plurality of recordingreproduction surfaces.
 6. The optical information recording methodaccording to claim 5, wherein the data recording starting position andthe data recording ending position respectively are determined to be thestarting position and the ending position in the data area of therecording reproduction surface where the front position of the sector isdisplaced most in a direction opposite to the scanning direction amongthe plurality of recording reproduction surfaces.
 7. An opticalinformation recording device for recording optical information in amultilayer optical disc including a plurality of recording reproductionsurfaces formed on every layer, with a sector structure having a gaparea arranged between an address area and a data area in a scanningdirection of an optical beam, wherein a bonding precision L withreference to a front position in the sector of a certain recordingreproduction surface and a length G of the gap area in the scanningdirection satisfies a relationship of L≦G for all recording reproductionsurfaces, the device comprising a detection part for detecting an amountof displacement between front positions in the sectors of otherrecording reproduction surfaces relative to the front position in thesector of the certain recording reproduction surface, and a gate signalgeneration part for generating a gate signal designating a datarecording ending position from a data recording starting position foreach recording reproduction surface to match the data recording startingpositions and the data recording ending positions of the respectivesectors in the plurality of recording reproduction surfaces, based onthe amount of displacement detected by the detection part.
 8. Theoptical information recording device according to claim 7, wherein thegate signal designates the data recording starting position and the datarecording ending position to be the starting position and the endingposition in the data area of the recording reproduction surface wherethe front position of the sector is displaced most in a directionopposite to the scanning direction among the plurality of recordingreproduction surfaces.
 9. A multilayer optical disc comprising layers onwhich a plurality of recording reproduction surfaces is formed, with asector structure having a gap area arranged between an address area anda data area in a scanning direction of an optical beam, bonded togethersuch that front positions in the sectors of the respective recordingreproduction surfaces are contacted closely to each other in thescanning direction by a predetermined precision, wherein guard datarecording areas having a length of not less than the predeterminedprecision are allocated to a tip portion and to a back end portion ofthe data area in the scanning direction.